Resilient bushing with long fatigue life

ABSTRACT

A resilient bushing with long fatigue life comprises an outer rigid member having curvilinear inner surface portions and inner rigid member having curvilinear outer surface portions. At least one of said surface portions has a surface roughness height rating measured by SAE Standard J448a. Said surface roughness height rating is provided by sandblasting said surface portions of a metal member, and thereafter forming on said surface portions a phosphate coating. An elastomeric insert is compressively positioned between said inner surface portions of the outer member and said outer surface portions of the inner member.

FIELD OF THE INVENTION

The present invention relates to a resilient bushing comprising innerand outer rigid members between which is positioned an elastomericinsert typically under radial compression.

BACKGROUND OF THE INVENTION

In the isolation of vibration between structural components, it hasbecome well known to use a resilient bushing having a pair of concentricrigid, typically metal sleeves. The inner sleeve is secured to onestructural component, and the outer sleeve is secured to the otherstructural component. An annular elastomeric insert is concentricallypositioned between the rigid sleeves typically under radial compression.Such resilient bushings are also utilized to increase the dampening ofmetal structures such as the frames of automobiles, and to interrupt lowimpedance all-metal paths for the transmission of structure-borne soundsin a metal structure. Illustrative of previously known resilientbushings and machines for making such bushings are those described inU.S. Pat. Nos. 2,749,160, 2,824,362, 2,840,893, 2,844,398, 2,858,155,2,872,727, 2,877,543, 2,895,215, 3,082,999, 3,147,964, 3,171,699,3,239,286, 3,380,791, 3,387,839, 3,560,034 and 3,643,320.

Originally these resilient bushings are made by inserting the uncuredelastomeric insert between the concentric sleeves and thereafterrelieving the internal stresses of the insert during bonding and curing.To increase the load-bearing capacity of the bushings, precured insertswere compressibly inserted between the sleeves. It was also found thatvarious spring rates in different radial directions could be achieved ina single bushing by providing the insert with various recesses.

One of the continuing difficulties with such resilient bushings has beenfatigue life. That is, the failure of the bushing after it has flexed agiven number of vibrational cycles. Fatigue failure is caused by therelative movement between the rigid members and the elastomeric insertand the resulting wearing away of the elastomeric insert. Thus, extendedfatigue life has been possible only where there is no relative movementbetween the metal sleeves and the elastomeric insert. Compressiveinsertion of precured elastomeric inserts between the sleeve members hasincreased fatigue life. However, it still remains common to specify arequired fatigue life in terms of a lower number of cycles e.g 100kilocycles, before failure.

Previously, resilient bushings have been made with phosphate coatedmetal sleeves. Phosphate coatings have been specified for manufacturingpurposes. The phosphate coating aided in assembly by holding a lubricantand preventing rust and corrosion of the sleeves after assembly. Thecoating weight and the corresponding surface roughness of the coatingvaried with the composition of the phosphate coating bath (e.g. anion,accelerator, etc.), the temperature of the coating bath, and the lengthof the coating cycle. However, for practical reasons, the phosphatecoating utilized has typically been between 700 and 900 milligrams/ft².Heavy phosphate coatings of greater than 2,000 milligrams/ft² have beenused to aid assembly and provide increased interference fit between theouter member and a control arm, etc., in certain applications. But, thecorresponding surface roughness height rating has not exceeded 170 RMSmeasured by SAE Standard J448a and has not been considered to havelasting effects because of the smoothing of the phosphate coating onassembly and subsequent use.

The present invention extends the fatigue life of resilient bushings bypreparation of the surfaces of the rigid members contacting theelastomeric insert. The preparation provides a surface roughness greaterthan previous bushings by sandblasting to reduce the movement betweenthe rigid members and the elastomeric insert.

SUMMARY OF THE INVENTION

A resilient bushing of the present invention comprises a rigid outermembers preferably in the form of a cylindrical sleeve, a rigid innermember preferably in the form of a cylindrical sleeve spaced apartpreferably concentrically from the outer member, and an elastomericinsert compressively positioned between said inner and outer rigidmembers. The outer member has curvilinear inner surface portions ofpreferably cylindrical shape and the inner member has curvilinear outersurface portions of preferably cylindrical shape.

At least one of said surface portions and most desirably the outersurface portions of the inner member is sandblasted to produce a surfaceroughness height rating of greater than 170 RMS and less than about 260RMS measured by SAE Standard J448a. Preferably the roughness heightrating of said surface is supplemented by subsequently forming on thesurface a phosphate coating of at least 2,000 milligrams per squarefoot.

Other details, objects and advantages of the invention will becomeapparent as the following description of the presently preferredembodiments and presently preferred methods of practicing the sameproceeds.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings, the preferred embodiments and presentlypreferred methods for practicing the invention are illustrated, inwhich:

FIG. 1 is an elevational view in cross-section of a resilient bushingembodying the present invention;

FIG. 2 is an exploded perspective view of the resilient bushing shown inFIG. 1;

FIG. 3 corresponds to FIG. 1 of SAE Standard J448a and shows the surfaceprofile of a precision reference specimen;

FIG. 4 corresponds to FIG. 2 of SAE Standard J448a and demonstrates themeasured profile of a surface; and

FIG. 5 corresponds to FIG. 3 of SAE Standard J448a and shows the meaningof each part of the symbols defined.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 1 and 2, a resilient bushing 10 is shown. Bushing 10comprises an outer rigid member 11 having a curvilinear inner surfaceportion 12 and inner rigid member 13 having a curvilinear outer surfaceportion 14. Preferably members 11 and 13 are made of metal such as steelor aluminum and are cylindrically shaped, and on assembly, arepreferably concentrically positioned with respect to each other.

Compressively positioned between members 11 and 13 is elastomeric,preferably annular insert 15. Elastomeric insert 15 can be made, forexample, by masterbatching an elastomeric compound with suitable amountsof accelerator, modifier and plasticizing agents as well as curingagents, accelerators, antioxidants and fillers. Suitable elastomericcompounds in addition to natural rubber are synthetic elastomers such asstyrene-butadiene rubber, ethylene-propylene rubber and the like,typically filled with carbon black. The masterbatch is injection,transfer or compression molded, and thereafter cured to form theelastomeric insert. The insert typically has a Shore-A hardness ofbetween 35 and 70 Durometer and most desirably of 50 Durometer orgreater.

The resilient bushing also includes preparing surface portions 12 and/or14 with a surface roughness height rating of between 170 RMS and about260 RMS measured by SAE Standard J448a. That is, either inner surface 12of outer member 11 or outer surface 14 of inner member 13, or both, isprepared prior to assembly of the resilient bushing with a surfaceroughness in the range above described. Preferably, as shown, at leastouter surface 14 of inner member 13 is provided with said surfaceroughness because the movement between the inner member 13 and theelastomeric insert 15 is higher, and in turn the wear is higher therethan the movement between outer member 11 and elastomeric insert 15.

Surface portions 12 and/or 14 are prepared with the desired surfaceroughness by sandblasting, and in addition coating said surface portionswith a heavy phosphate coating of at least 2,000 milligrams/ft². Theprocedures for sandblasting and phosphate coating of metals such assteel are old and well known to those skilled in the art and need not berestated here. The only point which needs repeating is that thesandblasting can be readily controlled to provide the desired lastingsurface roughness height rating measured by SAE Standard J448a.

SAE Standard J448a was first approved by the Surface Finish Committee ofthe SAE in March 1949 and was to applicants' knowledge last revised inJune 1963. The Standard states as follows:

1. General Data -- This SAE Standard is concerned with the geometricalirregularities of surfaces of solid materials. It establishes definiteclassifications for various degrees of roughness and waviness and forseveral varieties of lay. It also provides a set of symbols for use ondrawings, and in specifications, reports, and the like. The ranges forroughness and waviness are divided into a number of steps, and thegeneral types of lay are established by type characteristics.

This Standard does not define what degrees of surface roughness andwaviness or what type of lay are suitable for any specific purpose. Itdoes not specify the means by which any degree of such irregularitiesmay be obtained or produced. Neither is it concerned with the othersurface qualities such as luster, appearance, color, corrosionresistance, wear resistance, hardness, microstructure, and absorptioncharacteristics any of which may be governing considerations in specificapplications.

Surfaces, in general, are very complex in character. Although theheight, width, length, shape and direction of surface irregularities mayall be of practical importance in specific applications, this standarddeals only with the height, width, and direction.

2. Precision Reference Specimens -- Surface roughness designation bythis standard is based on instrument readings of surfaces to be rated incomparison with those of precision reference specimens having knownroughness values and having a wide distribution of replicas. Surfacesdescribed in the specifications for these specimens are designedprimarily to serve for calibration of instruments used for measuringsurface roughness height. They are not intended to have the appearanceor characteristics of commonly produced surfaces, nor are they intendedfor use in visual or tactual comparisons.

Specifications are given for surface contour, material, accuracy,uniformity, and rating that will be satisfactory for the purpose.

2.1 Surface Contour -- The normal surface profile of precision referencespecimens of roughness height shall consist of a series of isocelestriangles having included angles of 150 deg. Such a profile is shown inFIG. 3.

A departure from this triangular profile is permitted at the bottom ofthe grooves, provided that the deviated portion does not exceed 0.000130in. in width and that there shall be no solid material at any pointbeyond a line corresponding to a flat of this width. This departureshall not affect the portion above this flat, which portion shall meetthe allowed tolerance for accuracy.

2.2 Material -- The material from which precision reference specimensare made shall be such that repeated measurements on these specimens canbe made without significant loss of accuracy.

2.3 Accuracy -- Average roughness values of precision referencespecimens shall not vary from the designated value by more than ±1Mu in.or ±3%, whichever is the larger. The average spacing of the grooves ofprecision reference specimens shall be within 2% or 20 Mu in. (whicheveris the smaller) of the theoretical spacing corresponding to the nominalroughness height.

2.4 Uniformity -- The average deviation of roughness height ofindividual grooves of any precision reference specimen shall not exceed4% of the total roughness height. The average deviation of the groovespacings on a given precision reference specimen shall not exceed 3% ofthe average spacing.

2.5 Rating -- Precision reference specimens shall be rated for roughnessheight and roughness width as provided in the section on RecommendedValues of Roughness and Waviness of this Standard. With tracer typeinstruments having a finite tracer tip radius, it is impossible tobottom the ideally sharp grooves as described for the ideal triangularprofile. Accordingly, the proper reading of a tracer type instrument onthe precision reference specimens will depend on the tracer tip radius.Ratings of the specimens for checking the calibration of suchinstruments shall be supplied with the specimens..sup. 1 [¹ See alsoAppendix C in ASA B46. 1-1962.]

3. Definitions -- (See FIG. 5.)

3.1 Surface Texture -- Repetitive or random deviations from the nominalsurface which form the pattern of the surface. Surface texture includesroughness, waviness, lay, and flaws.

3.2 Surface -- The surface of an object is the boundary which separatesthat object from another object, substance, or space. Surfaces withwhich this standard is concerned shall be those requiring control ofroughness or other surface characteristics.

3.2.1 Nominal Surface -- Nominal surface is the intended surfacecontour, the shape and extent of which is usually shown and dimensionedon a drawing or descriptive specification.

3.2.2 Measured Surface -- The measured surface is a representation ofthe surface obtained by instrumentation or other means.

3.3 Profile -- The profile is the contour of a surface in a planeperpendicular to the surface, unless some other angle is specified.

3.3.1 Nominal Profile -- The nominal profile is the profile disregardingsurface texture.

3.3.2 Measured Profile -- The measured profile is a representation ofthe profile obtained by instrumental or other means. (See FIG. 4.)

3.4 Centerline (Roughness) -- The center is the line about whichroughness is measured and is a line parallel to the general direction ofthe profile within the limits of the roughness-width cutoff, such thatthe sums of the areas contained between it and those parts of theprofile which lie on either side of it are equal.² [² Centerline, asdefined above, is also known mathematically as the median line.]

3.5 Microinch -- One millionth of a linear inch (0.000001 in.). This isthe unit of height for roughness. Microinches may be abbreviated as Muin.

3.6 Roughness -- Roughness consists of the finer irregularities in thesurface texture usually including those irregularities which result fromthe inherent action of the production process. These are considered toinclude traverse feed marks and other irregularities within the limitsof the roughness-width cutoff. (See FIG. 5.)

3.7 Waviness -- Waviness is the usually widely spaced component ofsurface texture and is generally of wider spacing than theroughness-width cutoff. Waviness may result from such factors as machineor work reflections, vibration, chatter, heat treatment, or warpingstrains. Roughness may be considered as superposed on a wavy surface.Their directions are not necessarily related.

3.8 Lay -- The direction of the predominant surface pattern, ordinarilydetermined by the production method used.

3.9 Flaws -- Flaws are irregularities which occur at one place or atrelatively infrequent or widely varying intervals in a surface. Flawsinclude such defects as cracks, blow holes, checks, ridges, andscratches. Unless otherwise specified, the effect of flaws shall not beincluded in the roughness height measurements.

4. Specification and Rating

4.1 Roughness Height Rating -- The height of the roughness shall bespecified in microinches as the arithmetical average of the absolutedeviations from the mean surface. This value will be identified as aroughness number; for example, 16 means that the surface has anarithmetical average absolute deviation from the mean surface of 16 Muin.³ [³ Instruments calibrated in rms (root mean square) average willread approximately 11% higher on a given surface than those calibratedfor arithmetic average (aa).]

4.2 Roughness Width Rating -- The maximum permissible spacing ofrepetitive units of the dominant surface pattern. It may be specified ininches adjacent to the lay symbol. Irregularities having spacings up toand including the maximum specified are rated as roughness width and areto be included in the measurement of roughness height. When no maximumdimension is specified, spacings up to and including the width of theirregularities due to machine feed are rated as roughness width and areto be included in the measurement of roughness height.

4.3 Roughness-Width Cutoff -- The greatest spacing of repetitive surfaceirregularities to be included in the measurement of average roundnessheight. Roughness-width cutoff is rated in inches. Roughness-widthcutoff must always be greater than the roughness width in order toobtain the total roughness height rating.

Standard roughness-width cutoff values (inches) are:

    0.003   0.010   0.030   0.100   0.300   1.000

When no value is specified, the value 0.030 is assumed. Refer to SAEJ449, Surface Texture Control.

4.4 Waviness Height Rating -- Waviness heights may be specified directlyin inches as the vertical distance from peaks to valleys of waves.

4.5 Waviness Width Rating -- Waviness widths may be specified directlyin inches as the distance from peak to peak of the waves.

4.6 Lay Specifications -- The lay of a surface shall be specified by thelay symbol indicating direction of dominant visible surface marks.

5. Measurement or Evaluation -- For compliance with specified ratings,surfaces are to be evaluated by comparison with specified referencestandards or by direct instrument measurements as described below.

5.1 Roughness -- Roughness height values may be measured by anyacceptable method, for instance, sight, feel or instrument. For routinemeasurements, comparison may be made with a master surface thatsatisfactorily meets the requirements of the surface being measured. Inmaking comparisons care should be exercised to avoid errors due todifferences in material, contour, and type of operation represented bythe reference surface and the work.

In using instruments for comparison or for direct measurement, careshould be exercised to insure that the specified quality orcharacteristic of the surface is measured.⁴ [⁴ See ASA B46. 1-1962 forinstrument specifications.]

Roughness measurements, unless otherwise specified, are taken in thedirection which gives the maximum value of the reading normally acrossthe lay.

5.2 Waviness -- Waviness values for height and width may be measured byany suitable device for linear measurement.

6. Recommended Values of Roughness and Waviness -- The use of only onenumber shall indicate the maximum value of either the height or thewidth of irregularities. Any less degree shall be satisfactory. When twonumbers are used, they shall specify the maximum and minimum permissiblevalues.

    ______________________________________                                        SAE Roughness Height Values, Mu in.                                                  3       8     20   50    125   320    800                                     4      10     25   63    160   400   1000                              1      5      13     32   80    200   500                                     2      6      16     40   100   250   600                                     SAE Waviness Height Values, in.                                               0.00002  0.00008  0.0003   0.001 0.005 0.0.15                                 0.00003  0.0001   0.0005   0.002 0.008 0.020                                  0.00005  0.0002   0.0008   0.003 0.010 0.030                                  ______________________________________                                    

To illustrate the increased fatigue life with the present invention, thefatigue lives of three resilient bushings embodying the presentinvention were compared with corresponding production resilient bushingsused in automobile applications. The resilient bushings were similar tothe one shown in FIGS. 1 and 2 having an elastomeric insert under radialcompression of about 30 to 100% elongation. The Durometer of the naturalrubber compound used in the bushings was about 60 Durometer. Failure wasestablished by wearing away of the elastomeric insert until the outermember touched the inner member and made electrical contacttherebetween. The results of the tests are tabulated in TABLE I below.

    TABLE 1               ACTUAL          FATIGUE    ROUGHNESS-HEIGHT FATIGUE    RUN     LIFE TO   SURFACE PREPARATION OF OF OUTER SURFACE LIFE LOAD TOTAL CYCLES     TIME FAILURE TEST BUSHING OUTER SURFACE OF OF INNER MEMBER SPECIFIED (IN     ANGLE PER (IN (IN NO. NO. INNER MEMBER (IN ARMS) (IN CYCLES) POUNDS)     (DEGREES) HOUR HOURS) CYCLES)       .[.1.]. .[.1.]. .[.SANDBLASTED (#50 STEEL GRIT.].          .[.FOR AT     LEAST 3 MINUTES).]. .[.170-260.]. .[.--.]. .[.2250 ON O.M..]. .[.34 ON     I.M..]. .[.16,500.]. .[.79.0.]. 1,303,500.]. .[.2.]. .[.1.]. .[.SANDBLAST     ED (#50 STEEL GRIT.].   .[.FOR AT LEAST 3 MINUTES).]. .[.170-260.].     .[.--.]. .[.2250 ON O.M..]. .[.34 ON I.M..]. .[.16,500.]. .[.55.4.].     .[.914,100.]. .[.3.]. .[.1.]. .[.NONE - PLAIN STEEL.]. .[.10-50.].     .[.--.]. .[.2250 ON O.M..]. .[.34 ON I.M..]. .[.16,500.]. .[.44.4.].     .[.732,600.]. .[.4.]. .[.1.]. .[.NONE - PLAIN STEEL.]. .[.10-50.].     .[.--.]. .[.2250 ON O.M..]. .[.34 ON I.M..]. .[.16,500.]. .[.54.0.].     .[. 891,000.]. 5 2 SANDBLASTED (#50 STEEL GRIT FOR AT   LEAST 3 MINUTES)    .Iaddend. 170-260 200,000 470 ON O.M. 58 On O.M. 14,400 19.7 283,680 6 2    .Iaddend. 170-260 200,000 470 ON O.M. 58 ON O.M. 14,400 18.2 262,080 7 2    .Iaddend. 170-260 200,000 470 ON O.M. 58 ON O.M. 14,400 14.7 216,680 8 2    .Iaddend. 170-260 200,000 470 ON O.M. 58 On O.M. 14,400 18.9 272,160 9 2    .Iaddend. 20-50 200,000 470 ON O.M. 58 ON O.M. 14,400 12.9 185,760 10 2    .Iaddend. 20-50 200,000 470 ON O.M. 58 ON O.M. 14,400 12.0 172,800 11 2    .Iaddend. 20-50 200,000 470 ON O.M. 58 ON O.M. 14,400 14.4 207,360 12 2    .Iaddend. 20-50 200,000 470 ON O.M. 58 ON O.M. 14,400 14.9 214,560     .[.13.]. .[.3.]. .[.SANDBLASTED (#50 STEEL GRIT FOR.].   .[.AT LEAST 3     MINUTES).]. .[.130-260.]. .[.100,000.]. .[.1200 ON I.M..]. .[.40 ON     O.M..]. .[.16,500.]. .[.16.1.]. .[.265,650.]. .[.14.]. .[.3.]. .[.SANDBLA     NSTED (#50 STEEL GRIT FOR.].   .[.AT LEAST 3 MINUTES).]. .[.130-260.].     .[.100,000.]. 1200 ON I.M..]. .[.40 ON O.M..]. .[.165,00.]. .[.27.7.].     .[.457,050.]. .[.15.]. .[.3.]. .[.SANDBLASTED (#50 STEEL GRIT FOR.].     .[.AT LEAST 3 MINUTES).]. .[.120-360.]. .[.100,000.]. .[.1200 On I.M..].     .[.40 On O.M..]. .[.16,500.]. .[.23.3.]. .[.384,450.]. .[.16.]. .[.3.].     .[.SANDBLASTED (#50 STEEL GRIT FOR.].   .[.AT LEAST 3 MINUTES).].     .[.120-360.]. .[.100,000.]. .[.1200 ON I.M..]. .[.40 ON O.M..]. .[.16,500     .]. .[.32.1.]. .[.529,650.]. .[.17.]. .[.3.]. .[.SANDBLASTED (#50 STEEL     GRIT FOR.].   .[.AT LEAST 3 MINUTES).]. .[.120-360.]. .[.100,000.].     .[.1200 ON I.M..]. .[.40 On O.M..]. .[.16,500.]. .[.22.2.]. .[.366,300.].      .[.18.]. .[.3.]. .[.PHOSPHATE COATING (700-900 MG/FT.sup.2).]. .[.20-50.     ]. .[.100,000.]. .[.1200 ON I.M..]. .[.40 ON O.M..]. .[.16,500.].     .[.13.5.[. .[.222,750.]. .[.19.]. .[.3.]. .[.PHOSPHATE COATING (700-900     MG/FT.sup.2).]. .[.20-50.]. .[.100,000.]. .[.1200 ON I.M..]. .[.40 ON     O.M..]. .[.16,500.]. .[.14.1.]. .[. 232,650.]. .[.20.]. .[.3.]. .[.PHOSPH     ATE COATING (700-900 MG/FT.sup.2).]. .[.20-50.]. .[.100,000.]. .[.1200     ON I.M..]. .[.40 ON O.M..]. .[.16,500.]. .[.7.0.]. .[.115,500.].     .[.21.]. .[.3.]. .[.PHOSPHATE COATING (700-900 MG/FT.sup.2).]. .[.20-50.]     . .[.100,000.]. .[.1200 On I.M..]. .[.40 ON O.M..]. .[.16,500.].     .[.9.5.]. .[.156,750.]. .[.22.]. .[.3.]. .[.PHOSPHATE COATING (700-900     MG/FT.sup.2).]. .[.20-50 .]. .[.100,000.]. .[.1200 ON I.M..]. .[.40 ON     O.M..].  .[.16,500.]. .[.8.2.]. .[.135,300.]. .[.23.]. .[.3.]. .[.PHOSPHA     TE COATING (700-900 MG/FT.sup.2).]. .[.20-50.]. .[.100,000.]. .[.1200 ON     I.M..]. .[.40 ON O.M..]. .[.16,500.]. .[.7.8.]. .[.128,700.]. .[.24.].     .[.3.]. .[.PHOSPHATE COATING (700-900 MG/FT.sup.2).]. .[.20-50.].     .[.100,000.]. .[.1200 On I.M..]. .[.40 ON O.M..]. .[.16,500.]. .[.6.5.].     .[.107,250

As can be seen from TABLE I, the fatigue life of the resilient bushingsembodying the present invention were found to be consistently higherthan the fatigue life of the corresponding prior art bushings.Specifically, .[.the fatigue lives of the bushings of Tests Nos. 1-2(unrated) are higher than the fatigue lives of the bushings of TestsNos. 3-4;.]. the fatigue lives of the bushings of Tests Nos. 5-8 (ratedat 200 Kc) are higher than the fatigue lives of the bushings of TestsNos. 9-12.[.; and the fatigue lives of the bushings of Tests Nos. 13-17(rated at 100 Kc) are higher than the fatigue lives of the bushings ofTests Nos. 18-24.].. The advantage in fatigue life of the presentinvention over corresponding prior art bushings is clearly demonstrated.

While the presently preferred embodiments of the invention and means ofperforming them have been specifically described, it is distinctlyunderstood that the invention may be otherwise variously embodied andused within the scope of the following claims.

What is claimed is:
 1. A resilient bushing comprising:an outer rigidmember having curvilinear inner surface portions; an inner rigid memberhaving curvilinear outer surface portions; at least one of said surfaceportions being provided as a sandblasted surface with a phosphatecoating of selected weight of at least about 2,000 milligrams per squarefoot formed on said surface to define an effective roughness surfaceheight rating selected between about 170 RMS and 260 RMS in accordancewith SAE Standard J488a; and an elastomeric insert compressivelypositioned between said inner surface portions of the outer member andsaid outer surface portions of the inner member.
 2. A resilient bushingcomprising:an outer rigid member having curvilinear inner surfaceportions; an inner rigid member having curvilinear outer surfaceportions; at least one of said surface portions being provided as asandblasted surface with an effective phosphate coating formed on saidsurface to define an effective roughness surface height rating selectedin accordance with SAE Standard J448a; and an elastomeric insertcompressively positioned between said inner surface portions of theouter member and said outer surface portions of the inner member.
 3. Aresilient bushing as set forth in claim 2 wherein at least said outerportions of said inner rigid member is provided to define said roughnesssurface height rating.
 4. A resilient bushing as set forth in claim 2wherein said roughness height rating is selected to be at least about170 RMS.
 5. A resilient bushing as set forth in claim 2 wherein theweight of said effective phosphate coating is at least about 2,000milligrams per square foot.
 6. A resilient bushing as set forth in claim2 wherein said roughness height rating is selected between about 170 RMSand 260 RMS.
 7. A resilient bushing as set forth in claim 3 wherein saidroughness height rating is selected to be at least about 170 RMS.
 8. Aresilient bushing as set forth in claim 7 wherein the weight of saideffective phosphate coating is at least about 2,000 milligrams persquare foot.
 9. A resilient bushing as set forth in claim 3 wherein saidroughness height rating is selected between about 170 RMS and 260 RMS.10. A resilient bushing as set forth in claim 4 wherein the weight ofsaid effective phosphate coating is at least about 2,000 milligrams persquare foot.
 11. A resilient bushing as set forth in claim 5 whereinsaid roughness height rating is selected between about 170 RMS and 260RMS.
 12. A resilient bushing as set forth in claim 11 wherein at leastsaid outer portions of said inner rigid member is provided to definesaid roughness surface height rating.
 13. A resilient bushing as setforth in claim 1 wherein:at least said outer surface portions of theinner rigid member have said surface roughness height rating.